A $1 billion office-and-hotel tower being developed by Korean Air Lines in downtown Los Angeles will be the tallest building in the western US upon its completion in four years, according to the project's architect.

The foundation of the 335-metre tower will be poured at the end of this year, with a grand opening planned for March 2017, said Chris Martin, chief executive officer of Los Angeles-based architecture firm AC Martin Partners. The building will rise higher than downtown's 310-metre US Bank Tower, currently the tallest in the US West. Final renderings of the new tower were unveiled at a press conference on Thursday.

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"Downtown, along with a lot of the other commercial office centres, has relatively high vacancy rates as a result of the job losses stemming from the financial-market crisis," Robert Kleinhenz, chief economist at the Los Angeles County Economic Development Corporation, said. "But by the time this building opens it will probably be able to benefit from a recovery."

Downtown Los Angeles, which has undergone a decade-long revitalisation, has been helped by such developments as the Frank Gehry-designed Walt Disney Concert Hall on Grand Avenue, which has lured locals and tourists into the area since its 2003 opening. The Staples Centre sports arena, LA Live entertainment complex and new restaurants and bars also have drawn people to the area.

Vacancies rise

Even with the area's resurgence, office vacancies in downtown Los Angeles rose to 17.8 per cent in the third quarter, the latest period for which figures are available, from 15.6 per cent a year earlier, according to Jones Lang LaSalle Inc. The increase was mostly from the expiration of a Wells Fargo & Co lease at 444 S. Flower St., which resulted in 17,700 square metres coming on the market, the brokerage said in a report.

The Korean Air building will have 73 usable floors and feature a 30-metre-tall glass pediment and spire at the top. The tower will house a 900-room, four-star hotel; 37,000 square metres of office space; and 4200 square metres of retail space, according to AC Martin, a firm whose founder's projects included Los Angeles City Hall, completed in 1928 and featured in such television shows and movies as Dragnet, Adventures of Superman and LA Confidential.

The skyscraper will be built on the site of the Wilshire Grand hotel, which closed in 2011 and is being demolished. The project was scaled back from plans first announced in 2009 for two towers -- a 60-story office tower, and a 40-storey hotel.

The hotel's lobby will be located on the 70th floor, with restaurants on the 71st and an open-air pool on the 73rd. Instead of a helicopter landing pad on the roof, typical of most Los Angeles skyscrapers, the building will have a fireproof elevator encased in 3600 kilograms of concrete for emergencies, Martin said.

The project is expected to create more than 11,000 construction jobs and contribute $US80 million in tax revenue during development, according to its builders. More than 1700 permanent local jobs and $US16 million in annual local revenue will be created by the tower, they said.

"The new Wilshire Grand is an investment that makes sense and we are excited to continue our relationship with this great city," Korean Air Chairman Y.H. Cho said.